Dispenser cathode for cathode ray tube



pr 1964 J. T. McNANEY DISPENSER CATHODE FOR CATHODE RAY TUBE Original Filed Sept. 28, 1955 FLRXAO EKOWSQ DJPVIU C OU T "WZ WW I v H V.

ATTORNEY United States Patent 3 131 328 DEPENSER CATHSDE F1111 CATHQDE RAY TUBE Joseph T. McNaney, La Mesa, (Ialifi, assignor to General Dygamics Corporation, Rochester, N.Y., a corporation elaware Continuation of application Ser. No. 537,112, Sept. 28, 1955. This apfiication .iune 20, 19611, er. No. 37,801 3 Claims. (4C1. 313-337) This invention relates to a cathode of the dispenser type for a cathode ray display tube wherein the cathode has its emitting surface preformed into desired character configurations. More particularly, the invention pertains to a thermionic emissive cathode structure which is preformed into a predetermined set of characters. The resulting electron beam is utilized with cathode ray display tubes of the type generally shown in the copending application of I. T. McNaney, Serial No. 414,551, now U.S. Patent No. 2,761,988, assigned to the common assignee hereof.

This is a continuation of my copending application entitled Dispenser Cathode for Cathode Ray Display Tube, Serial No. 537,112, filed September 28, 1955, now abandoned.

In the past, cathodes of the non-dispensing type were formed by deposition of special oxide coatings on metallic surfaces. Shaping of these oxide coatings into a configuration of a desired character was possible. However, the coatings themselves were not sufficiently reliable as electron emitters to produce the shape of the character in an emitted beam. Further, the granular structure of the oxide coatings, such as thorium oxide compounds, limited the practicability of depositing and maintaining well defined and uniform electron emitting surfaces.

The present invention utilizes the dispenser type of cathode. One form of the dispenser cathode employs a mixture of powdered molybdenum tungsten alloy and a calcium barium aluminate compound which mixture may be pressed or molded into a desired shape and then sintered. I have found that by shaping the cross section of the cathode into a format of embossed areas forming a crosssection or matrix of characters upon the surface of the cathode; the cathode itself may then be utilized to form the electron beam including the particular character shapes embossed in the emitter. The dispenser cathode dispenses material to the surfaces thereof and will constantly rebuild the surface from within the cath ode. The emission of such cathode is uniform, therefore the character shaped cross-sections will always define the uniform character shaped beam with sufficient clarity and preciseness to provide a good character font on the screen of the display tube. The dispenser cathode may be advantageously utilized in combination with an aperture select system such as is illustrated in the aforementioned application of McNaney, Serial No. 414,551, now U.S. Patent No. 2,761,988.

Objects and advantages other than those set forth above will be apparent from the following description when read in connection with the accompanying drawings in which:

FIGURE 1 shows a cathode ray display tube embodying the invention.

FIGURE 2 is an enlarged cross section of the cathode.

FIGURE 3 is a plan view of the characters embossed into the cathode taken along line IIIIII of FIGURE 2.

FIGURE 4 shows a modified construction of the cathode of FIGURE 2.

FIGURE 1 shows a typical cathode ray display tube with an illustrative energizing circuitry, all of which are further exemplified in U.S. Patent No. 2,761,988. FIGURE 1 shows tube 11 wherein a cathode 11 is positioned at one end of the tube 10 for emitting an electron beam 12 toward a screen 13 at the opposite end of the tube. Positioned along the electron beam travel are a plurality of accelerating anodes 14, which may be either electrostatic or electromagnetic as is well known in the art, and is illustrated as electrostatic. The accelerating anodes 14 are utilized to accelerate and converge the shaped electron beam to a common point substantially intermediate a selection deflection means 15, which ineludes horizontal and vertical deflection plates 16, 17. These plates 16, 17 deflect the entire beam in conformance with control signals from a control unit 18 to position a desired character of the beam 12 at an aperture 19 of the apertured electrode 20.

The aperture 19 has a cross sectional size sufiicient to permit the cross section of a single character shaped beam 12 to pass therethrough. The single character shaped beam 12 is then deflected in response to signals from the control unit 18 by a positioning deflection means 21 to a desired position upon the screen. The position deflection means 21 may be either electrostatic or electromagnetic, but is shown in this instance as electromagnetic.

The invention more particularly refers to the cathode type and structure. The cathode 11 is shown in an enlarged cross section in FIGURE 2. The cathode 11 is generally comprised of an electron emitter 25 supported in a sleeve 28 of high temperature material such as tantalum, molybdenum and the like, and is in heat transfer relation to a heater 29. The heater 29 may be connected to any normal heater energizing source such as a D.-C. or A.-C. voltage source as is well known in the art. Between the heater 29 and the emitter 25 is a disc 30, of tantalum for example, Which acts as a barrier to prevent emission of electrons from the emitter 25 to the heater 29. Such a cathode 11 may have its emitter 25 preformed by molding or die-forming an emitting surface 26 into a character cross-section or format 27 as shown in FIG- URE 3. Each particular character cross-section 27 pre sents its own character shaped emitting surface 26. The entire format 27 composes the beam 12. Intermediate the emitting surfaces 26 is disposed a means 31 for selectively limiting emission of said emitter 25 to the surfaces 26. Means 31 may be a deposit of a high temperature non-emitting material such as rhodium, molybdenum or the like, which will prevent emission of electrons from the unembossed surfaces of the emitter 25.

The emitter 25 is preferably made of a mixture of powdered molybdenum-tungsten alloy and calcium barium aluminate compound. This mixture may then be preformed and molded, embossed or die cast into a desired shape. The mixture is then sintered. The final emitter 25 has the emitting surface 26 shaped into the format of cross sections 27 which emit shaped electron beams corresponding thereto. The actual emission of electron beam 12 is effected by the free barium supplied from the emitter 25 at the emitting surface 26. Application of heat to the emitter 25 causes the emitter material to diffuse free barium to the emitting surface 26 and effects a continual resupply for the life of the emitter.

Another embodiment of the cathode is shown in FIG- URE 4. Here the emitter 35 likewise is embossed and has the unembossed areas covered with the high temperature material 31 to prevent emission thereof. However, the manner of maintaining the barium in the emitting surfaces 26 diifers slightly. In this embodiment the source 36 of barium is placed in a cavity 37 below that of a porous tungsten emitter 35. Barium and strontium carbonates are initially supplied in the cavity 37. These will be decomposed by heat treatment given the cathode during activation to barium oxide and then to free barium. The barium is then diffused by the heat through the pores of the tungsten, thereby maintaining an active layer of emissive barium in the surfaces of the emitter 35. The

3 free barium then forms the active layer on the emitting surface 26 of the emitter 35.

In operation, the emitter either 25 or 35 is raised to a temperature of approximately 1250 C. by energizing the heater. At this temperature, barium is forced from the mixtures and a layer of barium is formed on the exposed surfaces and maintained by continued diffusion of barium to the surfaces of the emitter. The cathode 11, incorporated into the cathode ray display tube of FIGURE 1, provides the electron beam 12 of multiple cross sections 26. This beam 12 is accelerated and focused by anodes 14 to desired crossover areas. Adjacent one of the crossover areas, the selection means 15 is utilized to deflect the beam 12 to select a particular character shaped cross section 26 for presentation through the aperture 19 of the apertured electrode 29. This shaped beam 12 is then positioned by the positioning deflection means 21 to the desired position on the screen 13 of the cathode ray display tube 10.

The particular embodiment of the invention illustrated and described herein is illustrative only and the invention includes such other modifications and equivalents as may readily appear to those skilled in the art within the scope of the appended claims.

I claim:

1. In a cathode my display tube wherein an electron beam shaped into a plurality of individual spaced apart character-like cross sections is projected along the tube toward its screen, and wherein one of these cross sections is selected for impingement upon the screen, the improvement comprising the means for generating the electron beam wherein such means includes a cylindrical sleeve, a heater inserted into one end of the sleeve and in heat radiating cooperation therewith, and an electron generating construction for providing the electron beam positioned within and adjacent the other end of the sleeve, the construction being heated by the heat radiated from the heater and preventing electron emission from the heater to the other end of the sleeve, the construction including a free barium electron carrier emitter whose emitting surfaces are preformed into the plurality of individual spaced apart character-like cross sections, which emitting surfaces emit electrons forming the electron 4,- beams, and means placed over and upon the nonformed portions of the emitter and positioned with the other end of the sleeve at its terminus for preventing electron emission of said emitter from areas other than the plurality of character-like cross sections.

2. In a cathode ray display tube wherein an electron beam shaped into a plurality of individual spaced apart character-like cross sections is projected along the tube toward its screen, and wherein one of these cross sec tions is selected from impingement upon the screen, the combination comprising: a free barium electron carrier emitter whose emitting surfaces are preformed into a plurality of individual spaced apart character-like cross sections, which emitting surfaces emit electrons forming the electron beam; means placed over and upon the nonformed portions of the emitter for preventing electron emission of said emitter from areas other than the plurality of character-like cross sections; a heater adjacent said emitter and in heat radiating cooperation therewith, said emitter being heated by the heat radiated from said heater.

3. In a cathode ray display tube wherein an electron beam shaped into a plurality of individual spaced character-like cross-sections is projected along the tube toward its screen, and wherein one of these cross-sections is selected for impingement upon the screen, the combination comprising: a cathode body having electron emitting surfaces preformed into a plurality of individual spaced character-like cross-sections, the electrons from said emitting surfaces forming said electron beam; means positioned over the nonformed portions of said cathode body for preventing electron emission from areas other than the plurality of character-like cross-sections; and heater means adjacent said cathode body for indirectly heating said cathode body.

References Cited in the file of this patent UNITED STATES PATENTS 2,254,095 Thompson Aug. 26, 1941 2,272,165 Varian et al. Feb. 3, 1942 2,459,841 Rouse Jan. 25, 1949 2,883,576 Harries Apr. 21, 1959 2,895,070 Espersen July 14, 1959 

3. IN A CATHODE RAY DISPLAY TUBE WHEREIN AN ELECTRON BEAM SHAPED INTO A PLURALITY OF INDIVIDUAL SPACED CHARACTER-LIKE CROSS-SECTIONS IS PROJECTED ALONG THE TUBE TOWARD ITS SCREEN, AND WHEREIN ONE OF THESE CROSS-SECTIONS IS SELECTED FOR IMPINGEMENT UPON THE SCREEN, THE COMBINATION COMPRISING: A CATHODE BODY HAVING ELECTRON EMITTING SURFACES PREFORMED INTO A PLURALITY OF INDIVIDUAL SPACED CHARACTER-LIKE CROSS-SECTIONS, THE ELECTRONS FROM SAID EMITTING SURFACES FORMING SAID ELECTRON BEAM; MEANS POSITIONED OVER THE NONFORMED PORTIONS OF SAID CATHODE BODY FOR PREVENTING ELECTRON EMISSION FROM AREAS OTHER THAN THE PLURALITY OF CHARACTER-LIKE CROSS-SECTIONS; AND HEATER MEANS ADJACENT SAID CATHODE BODY FOR INDIRECTLY HEATING SAID CATHODE BODY. 